Antenna device and transmitter-receiver using the antenna device

Abstract

An antenna device of transmission line type having two antenna elements opposed to each other, and a signal is fed between the two antenna elements. A variable-capacitance unit capable of changing the electrostatic capacity is provided at one or both of connection points at which opposite ends of the two antenna elements are connected to each other. Each variable-capacitance unit has a variable-capacitance diode, the electrostatic capacity of which changes according to a direct-current voltage applied between the anode and the cathode.

1. An antenna device of transmission line type comprising:
 two antenna elements opposed to each other, a signal being fed between said two antenna elements; and 
 a variable-capacitance unit capable of changing the electrostatic capacity, said variable-capacitance unit being provided at one or both of connection points at which opposite ends of said two antenna elements are connected to each other. 
 
   
   
     2. The antenna device according to  claim 1 , wherein a length of each of portions of said two antenna elements on opposite sides of a feed point is equal to or smaller than ¼ of a wavelength of the fed signal. 
   
   
     3. A transmitter-receiver comprising the antenna device according to  claim 2 , the antenna device being mounted along peripheral side portions of a frame. 
   
   
     4. The antenna device according to  claim 1 , wherein said two antenna elements are spaced apart from each other by a distance smaller than a wavelength of the fed signal. 
   
   
     5. A transmitter-receiver comprising the antenna device according to  claim 3 , the antenna device being mounted along peripheral side portions of a frame. 
   
   
     6. The antenna device according to  claim 1 , wherein said variable-capacitance unit comprises a variable-capacitance diode, an electrostatic capacity of which changes according to a direct-current voltage applied between an anode and a cathode, and a predetermined direct-current voltage is applied to the variable-capacitance diode from a voltage control unit. 
   
   
     7. A transmitter-receiver comprising the antenna device according to  claim 6 , the antenna device being mounted along peripheral side portions of a frame. 
   
   
     8. A transmitter-receiver comprising the antenna device according to  claim 1 , the antenna device being mounted along peripheral side portions of a frame. 
   
   
     9. The antenna device of  claim 1 , wherein said two antenna elements form a pair of parallel lines and said parallel lines are bent in other than a straight line. 
   
   
     10. The antenna device of  claim 1 , wherein said variable-capacitance unit comprises a trimmer capacitor. 
   
   
     11. The antenna device of  claim 1 , wherein each said variable-capacitance unit is located along said two antenna elements at approximately an integer multiple of ½ of a wavelength of a fed signal. 
   
   
     12. An antenna device of transmission line type comprising two antenna elements opposed to each other, a signal being fed between said two antenna elements, wherein said two antenna elements are spaced apart from each other by a distance smaller than a wavelength of the fed signal, wherein a length of each of portions of said two antenna elements on the opposite sides of a feed point is equal to or smaller than ¼ of a wavelength of the fed signal. 
   
   
     13. The antenna device according to  claim 12 , wherein said two antenna elements comprise a variable-capacitance unit capable of changing an electrostatic capacity, said variable-capacitance unit being provided at one or both of connection points at which opposite ends of said antenna elements are connected to each other. 
   
   
     14. The antenna device according to  claim 13 , wherein said variable-capacitance unit comprises a variable-capacitance diode, an electrostatic capacity of which changes according to a direct-current voltage applied between an anode and a cathode, and a predetermined direct-current voltage is applied to the variable-capacitance diode from a voltage control unit. 
   
   
     15. A transmitter-receiver comprising the antenna device according to  claim 14 , the antenna device being mounted along peripheral side portions of a frame. 
   
   
     16. A transmitter-receiver comprising the antenna device according to  claim 13 , the antenna device being mounted along peripheral side portions of a frame. 
   
   
     17. A transmitter-receiver comprising the antenna device according to  claim 12 , the antenna device being mounted along peripheral side portions of a frame. 
   
   
     18. The antenna device of  claim 12 , wherein said two antenna elements form a pair of parallel lines and said parallel lines are bent in other than a straight line. 
   
   
     19. An antenna device of transmission line type comprising two antenna elements opposed to each other, a signal being fed between said two antenna elements, wherein said two antenna elements are spaced apart from each other by a distance smaller than a wavelength of the fed signal, the antenna device being mounted along peripheral side portions of a frame.